Other than Wow Art, there's Rus http://www.rus-art-studio.com/ (level 2 of the shophouse, near Liquid Kitchen... same side as Long House (so it's diagonal across Wow Art)),
and another one behind the Kampong Chicken / Dino's and it's called Art Grain.

Rus Art has been around for a long while but only moved to this location this year.

Not familiar with Art Grain - was told by a friend and saw the studio from outside... didn't explore at all.